1. Field of the Invention (Technical Field)
This invention relates to a precipitation gauge of a type that collects liquid and frozen precipitation and accurately measures the accumulation thereof.
2. Background of the Invention
It is well known to measure rainfall for a variety of purposes including immediate and historical data for use in agriculture and other human activities including the satisfaction of curiosity. When high accuracy is required, a number of problems arise in providing a device and method for measuring precipitation. Among these problems are the necessity of precisely converting the weight or volume of collected precipitation to a measurement typically given in inches of precipitation. In many instances it is desirable to measure the precipitation in remote areas where manual attendance is difficult and it therefore is desirable to provide a means and a method for transmitting the measurements from the remote site. Operation of a remote measurement device also may entail transmitting messages from a central site to the remote site for a variety of purposes. In such remote applications it is extremely important that mechanical malfunctions of the measuring device or gauge be minimized. It may also be desirable to measure both total accumulated precipitation during a fixed period as well as incremental accumulation, thereby providing a rate of precipitation during a selected period. Where the remote device is placed in an environment where there is wide temperature differences, it will be necessary to compensate the measurement of precipitation to accommodate the variations in temperature. It is also necessary to be able to calibrate the gauge from time to time. And since such gauges may be portable, or relatively portable, it may be practically necessary to provide overload and shock protection for what is inherently a delicate instrument.
While all of these difficulties are encountered in rain measuring devices, a major problem is the need to measure both rain and snowfall. Snow measurement problems include assuring that the snowflakes are converted to a liquid equivalent which is the typical way in which precipitation is expressed. Other problems include the possibility of snow accumulation in the opening of the reservoir or container in which the precipitation is accumulated over a prolonged period of time. Additional problems are encountered where the snowfall is accompanied by wind whereby the wind forces the snow against a portion of the opening of the container resulting in a decrease in the opening which adversely affects the calculation of the precipitation since the calculation is dependent upon a measurement that is based on a fixed area in which the precipitation is collected. Similar problems may exist with freezing rain.
3. Background Art
Many of the above-described problems have been addressed in one manner or another in the prior art, though many other problems remain to be solved. The most simple type of precipitation gauge measures rain by permitting the accumulation of the liquid in a container which in turn operates a float or a device that indicates hydrostatic pressure. Such device is shown in U.S. Pat. No. 2,509,522 which shows a simple visual indicator of accumulated rainfall based on indicia marked on a transparent receptacle. A float-type gauge with indicia to indicate the level of the float is shown in U.S. Pat. No. 5,245,874 where the float utilizes optical means to determine the height of the float and converts optical signals into electrical signals which may be transmitted. Another float-type device with a visible cylindrical container is shown in U.S. Pat. No. 5,038,606. Still another rainwater gauge is shown in U.S. Pat. No. 4,233,841 which includes an elongated hollow, open-ended cylinder including a funnel which directs the rainfall into a graduated measuring tube and in which the inner surface of the opening, including a funnel, of the cylinder is coated with a hydrophobic material so as to assure that all of the rain is deposited into the graduated tube. Still another device discloses a particular type of collector system wherein one container is filled to its capacity, and then overflows into a second container whereby the accumulation is a measurement of the volume of the first container plus the portion of the volume of the second container that contains the precipitation. Other devices, such as that shown in U.S. Pat. No. 4,895,022 are primarily concerned with mitigating the effects of winds on precipitation measurement by attempting to minimize the disturbance of the wind and wind-borne rain due to the very presence of the gauge. One device that is particularly designed to cope with the problems involved in the measuring of snowfall as well as rainfall is shown in U.S. Pat. No. 5,571,963 in which the container is partially filled with antifreeze which, of course, reduces the snowflakes to their liquid equivalent without the requirement for any heating means; the patented device also utilizes a spring weighing mechanism.